Cold Agglutinin Syndrome Caused by Mycoplasma pneumoniae in a Recipient of a Renal Transplant

Cold agglutinin syndrome (CAS) is a secondary autoimmune hemolytic anemia caused by complement activation at low temperatures. Although Mycoplasma pneumoniae–related CAS is recognized in immunocompetent hosts, its occurrence in adult recipients of solid organ transplants is rarely reported. We describe a recipient of a renal transplant receiving tacrolimus-based immunosuppression who developed CAS after M pneumoniae infection, which presented as isolated anemia without respiratory symptoms. Hemolysis resolved with supportive care while immunosuppressive therapy was maintained. This case highlights that infection-caused, complement-mediated hemolysis can occur despite pharmacologic immunosuppression and underscores the need to consider CAS in posttransplant anemia.